Hadith 1682 - The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day - Sunan An-Nasa'i - سنن النسائي - Collection of Actions, Sayings and Teachings of Prophet Muhammad (صلى الله عليه و سلم) - Kutub as-Sittah

20. The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day - كتاب قيام الليل وتطوع النهار

30) Chapter: The time for witr

It was narrated that Ibn 'Umar said: "Whoever prays during the night, let him make the last of his prayers at night witr, because the Messenger of Allah (ﷺ) used to enjoin that."

Reference: 1682
English reference: Vol. 2, Book 20, Hadith 1683
In-book reference: Book 20, Hadith 85
Grade: Sahih (Darussalam)
Read this hadith from Darussalam Collection

30) باب وَقْتِ الْوِتْرِ

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ نَافِعٍ، أَنَّ ابْنَ عُمَرَ، قَالَ مَنْ صَلَّى مِنَ اللَّيْلِ فَلْيَجْعَلْ آخِرَ صَلاَتِهِ وَتْرًا فَإِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَأْمُرُ بِذَلِكَ ‏.‏